Single Side Band (SSB) direct detection system is considered as an attractive solution for 80 km Data Center Interconnects (DCI), due to its characteristics of low-cost, simple system architecture, and high robustness to chromatic dispersion. However, Signal to Signal Beating Interference (SSBI) is the major problem in SSB direct detection system. In order to address the SSBI in the SSB direct detection systems, the SSB modulation realized by IQ modulator and Dual Drive Mach Zehnder Modulator (DDMZM) is investigated. A SSB signal reconstruction algorithm based on time domain iteration and an SSBI-free direct detection scheme based on DDMZM are proposed respectively for these two SSB direct detection systems. The implementation principle and simulation or experimental setup are introduced in detail. According to the simulation and experimental results, the effectiveness and feasibility of the two schemes in SSBI elimination are discussed.